I've seen a few threads about this, but nothing that answers my specific questions. Heater takes a while to warm up, and I'm pretty sure the problem is there is no vacuum at the heater control valve. I have a new valve, new therm, and new heater core. Also, nothing happens when you flip it to "max", but it looks like all the other functions seem to work as they should, it just takes the heater longer to warm up because the little plunger valve in the bypass is not opening due to no vacuum. The only hot water that's in the heater core then is kind of a backwash I guess, no circulation? I've read the black vacuum line is the heater, but I don't see black on my selector wheel. I see blue, red, orange, tan and pinkish I think, maybe purple. I tried to follow the control valve line through the firewall to test it, but can't find it in the inside. I saw a YouTube link on another thirdgen thread showing how to repair the wheel with a bolt and nut. I can do that if that's the issue, but how do I know? Before I tear it apart, I thought I'd get some more facts/opinions. I can hear the hissing when I turn the selector to off, and sometimes between functions, so that may mean there's a leak. I don't think you can get the vacuum wheels anymore can you? BTW, my car is a 92 Formula if that helps.

 

Just spent $18.99 incl shipping on what looked like a decent controller from another 92 Firebird on eBay. If nothing else, it will give me something to look at to better understand the one that's in the car, and it may work as a replacement if mine is broken. For that price, not much to lose.

 

You can also delete the HCV, heater will work well. Downside is it heats the box when ac is on so loose ac cooling power. If the ac doesn't work anyway....
The heater core may be packed with sludge. If the HTC hasn't worked in a long time, the lack of coolant circulation in the core gums it up.
I'm not sure, but I think I remember the vac line from the firewall is orange, then goes to a t, then black to the HTC. Can't remember what the other line from the t goes to.

 

These may help you, under the hood portion anyhow.

 

No, I have a new therm, new heater valve and new heater core, so it shouldn't be gummed up anywhere. New hoses for the most part too. There are two vacuum lines under the hood from out of the harness--one to the hcv, and I think the other line comes up to a T and goes to the cruise control and I forget where else, probably plenum or tb. The only lines I see under the hood are black, but the line at the passengers side of the hvac "valve" under the kick panel is orange, drivers side valve is tan. I assume one is ac, one is heat. But what I couldn't find was the juncture where the black becomes orange? I don't even know if the ac even works in this car, I don't think it does, although it was an Arizona car, so I'm sure it was used last summer(2013). I bought it last winter, and drove it all summer without using the ac. I almost never use ac in any of my cars, especially since I own 2 cars with t-tops! I thought about deleting the hcv, but since I just bought a new valve I didn't want to let it go to waste. LOL The "new" controller arrived today, we'll see if there's anything I can learn from it.

 

New controller looks like a good unit. Very clean, everything where it should be. The vacuum selector wheel needs a new center clip, but an airplane nut and bolt will fix that. Needs new bulbs and a little cleaning up, but looks like a steal for what I paid for it. In fact, it looks way better than the one that's in my car right now! But this looks really simple now that I can tear it down and see how it works. Once I get this rebuilt and installed, and check the vacuum lines, everything ought to work like new.

 

No dice. Put the new unit in, and got full time defrost--so there's an issue with it too. I never had that problem with my old unit, so I'm hoping I can put enough parts together from the two to get one good one. I could be wrong, but I wonder if the full time defrost has something to do with the electronics on the function selector wheel on top? I was gonna pull it apart too, but didn't. Looks like I better now, I can always put it back together with a nut/bolt if the clip breaks. I saw something about full time defrost on another hvac thread, I'll see if I can dig it up. Now, on my old one all the functions worked normally except when you put it on "max", where nothing happened. Another thing that I found was that it was a royal pain in the butt to try to ge the right shape on the blend door wire!

 

Ok, the other thread says defrost only is a vacuum line issue. But which one? Main line from the engine? That's the purple one I think? And if it's a vacuum line issue, why did it not do this with the old controller?

 

Its gonna be one of the two hard lines under hood at firewall. One goes straight to heater control valve, the other goes to ported vacuum. If it don't work one way, switch the tubes.

 

Yeah, but that can't be. It only started doing this when I put the "new" controller in. With my original I had no vacuum at the heater control valve, that was why I changed it. I know about the two lines under the hood, but that doesn't explain why all the sudden I got full time defrost when I put the second controller in! And when you say switch the tubes, do you mean flip the double vacuum line connector at the heat/ac switch where the blend door wire connects to the controller? You think maybe I put that dual vacuum line plug on backwards? Would that give you full time defrost? Or do you mean switch the lines at the T under the hood? Not sure I understand, are we talking about two different issues here?

 

We're on the same page. If the connector is backward at the controller, it could be it. Do you have ANY vacuum at the controller? Vacuum is needed to close that door in the system; with engine running of course. IDK, I'm think'n

 

Well, everything worked on the old controller except the max setting, so there was vacuum then at least. It toggled between all the settings just fine, it just took longer than it should to warm up apparently because there was no vacuum at the heater valve. Btw, I have new therm, new heater core and heater valve. Maybe I jiggle a line loose when I was doing the swap. IDK.

 

Btw, the engine was not running when I checked this today. I just turned the key to the on position and got defrost at every setting. But I still don't think that would keep the settings from working right if everything is good.

 

I thought the engine HAD to be running to create the vacuum to operate the bypass door???

 

I had several issues with my controls in my 92 RS... The hissing sound is definitely a vacuum leak at the controls. I had to do the small bolt and nut repair on the valves. I also had to replace the switch as it had a deteriorated and a loose electrical connection that overheated. I never had any problems with the line from the heater control valve through the firewall except once when the EGR valve went bad. The EGR valve started leaking and shot hot exhaust gas onto the vacuum line to the heater control valve and melted it in two.... All of my issues with only having defrost, not switching and the blower intermittent were caused by the switches, both electrical and vacuum, on the environmental control module. I pulled my stereo and then pulled the control module out so I could work with it while the car was running. It's a bit of a pain due to some of the cables but it made it much better to diagnose. If you pull it apart, probably a good idea to replace the electrical switches due their age if they are original. The electrical contacts carry a lot of current and with oxidation and wear they can loosen and heat up over time.. Mine actually got hot enough to melt some of the plastic on the switch. I essentially restored mine and it has been working fine ever since..

 

I don't think so because you can turn the key to the acc or on position and blow the vents, heater or defroster. You would need vacuum to open the hcv though.

 

Ok, my original one has some melting on the top where the "1-5" electrical connections are--the ones that toggle when you select different functions with the top slider. However, that being said, the only function that actually doesn't work is the max function, and I had no defrost only issue with it. No vacuum at the hcv was my motivation in changing it. The "new" one (out of another 92 with 120k on it) has no melting and looks good pretty much all around. I went ahead and did the nut and bolt fix on the main vacuum wheel, seems like it's ok, didn't hear any leaking on it. Could also be those 1-5 selector connections are needing to be redone. Now, how do I "rebuild" them? Is it just a matter of cleaning/resurfacing or what? I can take it apart tonight and have a look. I was gonna do that before, but decided I'd install it and see what worked before I borrowed trouble. And yeah, I had it halfway out while still connected messing with it flipping switches and etc while turned on yesterday too. If I can get it off constant defrost I'll feel like I've made progress. BTW, any tips you can offer me on the shape of the wire to the blend door would also be welcomed. I went ahead and took the wire off my old unit and will re-use it because it had a better shape to it. The wire off the replacement unit is almost straight at the end, I'd have to re-engineer the proper angles. Pain in the rear.

 

I just pulled apart the switch in the replacement controller, and I'm not sure what I'm looking at. The springs and contacts look like they're in decent shape, what do I need to look for? That inner copper section that the contacts slide over? Doesn't look TOO bad, but it does have some minor scuffing and discoloration. Here's a pic.

 

Here's a pic of the original switch from the first controller. I haven't opened it yet, shows the melt damage. But other than the max setting, THIS switch seems to work. Go figure.